System Performance Test

Figure 19: Pressure-Temperature Relationship Conditions Equivalent To 30 MPH Or 1750 Engine RPM:

The system should be operated for at least 15 minutes to allow sufficient time for all parts to become completely stabilized. Determine if the system is fully charged by the use of test gauges and sight glass if one is installed on system. Head pressure will read from 1241-1516 kPa (180-220 psi) or higher, depending upon ambient temperature and the type of unit being tested. The sight glass should be free of bubbles. Low side pressures should read approximately 103-206 kPa (15-30 psi), depending on the ambient temperature and the unit being tested. The type of control and component installation used on a particular system will directly influence the pressure readings on the high and low sides.


The high side pressure will be affected by the ambient or outside air temperature. A system that is operating normally will indicate a high side gauge reading between 1034-1172 kPa (150-170 psi) with an 26.7° C (80° F) ambient temperature. The same system will register 1447.9-1585.8 kPa (210-230 psi) with an ambient temperature of 37.8° C (100° F). No two systems will register exactly the same, therefore, allowance for variations in head pressures must be considered.